A secondary battery which has ease with applicability for various product groups and good electric characteristics such as high energy density is universally applied not only to portable devices but also electric vehicles (EV), hybrid electric vehicles (HEV), energy storage systems or the like, which are driven by an electric source. The secondary battery has a primary advantage of greatly reducing the use of fossil fuels and a secondary advantage of generating no byproduct after the use of energy, and thus the secondary battery receives attention as a new energy source which is environment-friendly and promotes energy efficiency.
A battery pack applied to an electric vehicle or the like includes a plurality of cell assembly connected in series, each cell assembly having a plurality of unit cells, in order to obtain high output. In addition, the unit cell includes positive and negative electrode current collectors, a separator, active materials, an electrolyte or the like and is capable of being repeatedly charged and discharged by means of electrochemical reactions among the components.
In addition to such a basic structure, the battery pack may additionally include a battery management system (BMS) for monitoring and controlling a state of the secondary battery by applying an algorithm for controlling a power supplied to a driving load such as a motor, measuring electric characteristic values of current or voltage, controlling charge/discharge, controls voltage equalization, estimating a state of charge (SOC), or the like.
Meanwhile, recently, as the necessity for a large-capacity structure to be utilized as an energy storage is increasing, the demand for a battery pack having a multi-module structure in which a plurality of modules, each having a plurality of secondary batteries connected in series and/or in parallel, are aggregated is also increasing.
In the battery pack of a multi-module structure, a plurality of secondary batteries are densely arranged in a narrow space, and thus it is important to easily emit heat generated from each secondary battery. Japanese Unexamined Patent Publication No. 2009-301877 discloses an indirect cooling method, as one of various methods for emitting the heat generated from a secondary battery.
In the indirect cooling method, a cooling fin in contact with a package material of a secondary battery is cooled by means of a coolant. The heat generated from a secondary battery is transferred through the cooling fin, and the cooling fin transfers the heat to the coolant again, thereby preventing the secondary battery from being heated. The cooling fin is coupled to a frame and disposed at a battery system.
However, if the cooling fin and the frame are made of different materials, a coupling region between the cooling fin and the frame may cause a leakage, which may cause leakage of a part of the coolant, and thus resultantly the secondary battery may be heated.